1. Field of the Invention
The present invention relates to a detection device having photosensitivity in a near infrared wavelength range and a method for manufacturing the detection device.
2. Description of the Related Art
In a detection device including a photodiode array in which photodiodes are arranged, read-out electrodes of signal read-out silicon IC (ROIC: Read Out IC) face electrodes of the arranged photodiodes, and electric conduction is made by bumps provided between the two types of electrodes. In a near infrared range or infrared range on the longer wavelength side than a visible range, the photodiodes are formed using a compound semiconductor. Therefore, such a configuration may be referred to as a “hybrid configuration” including a compound semiconductor and silicon (IC). Crystals of the compound semiconductor are weak against mechanical force, and thus indium (In) which is soft and has a low melting point is frequently used for bumps when the hybrid configuration is formed.
Indium bumps are easily deformed and made nonuniform due to the above-described property when provided on photodiode electrodes or ROIC read-out electrodes. For example, the indium bumps do not have a uniform cylindrical column shape but frequently have a shape which has a burr projecting along the edge of the top or a shape which is broken on one of the sides to be deformed into a frustum. Although several tens of thousands to several hundreds of thousands of bumps are provided on a detection device, bumps having large shape deviation are necessarily produced. In pressure bonding or brazing and welding, one-to-one conduction is not realized with bumps having large shape deviation, and such bumps easily project from the regions of the bumps (corresponding pixel regions) and contact adjacent bumps or do not realize one-to-one conduction. Such defective pixels become white spots on a black-background screen, and disconnected pixels become black spots on a white-background screen. The defective pixels cause undesirable imaging or cause deterioration of resolution in material detection or inspection, thereby decreasing the commercial value of a detection device.
In order to resolve the above-mentioned problem, many proposals have been made. In order to control the shapes of In bumps to be uniform in the hybrid configuration, there has been proposed (d1) a method of making it easy to control In bump shapes to be uniform by heat melting an evaporated film of In whose melting point decreased by alloying during liftoff, (Japanese Unexamined Patent Application Publication No. 5-136147). Also there has been proposed (d2) a method of providing an engagement structure using irregular portions between a compound semiconductor substrate and a silicon substrate in order to prevent lateral deviation during bonding of bumps in a hybrid configuration (Japanese Unexamined Patent Application Publication No. 7-38076). Further there has been proposed (d3) a method of incorporating a gap adjusting member for providing an appropriate gap in the vertical direction (thickness direction), thereby preventing defective bonding of bumps during bump bonding (Japanese Unexamined Patent Application Publication No. 2002-299650). Further there has been proposed (d4) a method of placing bumps in holes in a reticular-pattern member composed of an insulating resin so that the bumps are surrounded by a non-hole portion and are isolated from adjacent bumps (Japanese Unexamined Patent Application Publication No. 7-153905).
The above-described improvement methods (d1) to (d4) have the following problems.
(d1)(i) The application is limited. In this method, the melting point of 160° C. of In is further decreased, and thus the bumps having the decreased melting point cannot resist the heat generated by IC, summer atmospheric temperature, and the like. Therefore, the application is limited to infrared sensors used by cooling, such as MCT (Mercury Cadmium Telluride (HgCdTe)). In addition, from the viewpoint of preventing re-melting of bumps which causes short-circuiting between pixels, it is necessary to select a material with a lower melting point as a die bonding material for mounting the resultant hybrid configuration on a package and as a joint material used for jointing a lid to the package and sealing it, thereby significantly decreasing the number of options. (ii) When In is evaporated, the amount of In evaporated varies with positions, and thus it is difficult to control the heights of In bumps to be uniform. For example, even when In bumps are formed on both a photodiode and ROIC in order to absorb variation of height, the tops of the In bumps slip during bonding because the tops are not flat. This may cause short-circuiting between pixels.
(d2) The cost is increased. In order to form an irregularity engagement structure, it is necessary to form a mask pattern on both a compound semiconductor substrate and a silicon substrate and perform dry etching. Therefore, the number of steps is increased.
(d3) The bonding yield is decreased. During bonding with In bumps having variations in height and shape, bonding variation occurs in an early stage of bonding.
(d4) The bonding yield is decreased. Although short-circuiting due to lateral deviation can be prevented by the non-hole portion of the reticular pattern, short-circuiting due to overflow, which is caused by variation in height, or disconnection in a portion having an insufficient height cannot be suppressed.